Fault Models SSC TI Team Evaluation Hans AbramsonWard

Transcription

1 1 Fault Models SSC TI Team Evaluation Hans AbramsonWard PG&E DCPP SSHAC Study

2 2 Outline Constraints on location of active faults: Uplift of ranges Quaternary fault map Constraints on Depth of seismogenic faulting Distribution of hypocentral depth Constraints on fault dip Scaled to dimensions of uplift Awaiting evaluation of PE models for microseismicity and seismic reflection data Fault models: Illustrate simplification of surface traces into fault sources while describing underlying concept behind fault model Video tour of 3d fault model geometry illustrating linkages and relationships Accounting of fault parameters for PSHA

3 Data to Constrain Uplift Rates 3 >0 Approximate uplift rates, mm/yr 0.20 > <0

4 4 Offshore faults from hi-res 2D seismic reflection data Activity assessed on every line, ~800 m spacing -inferred from deformation of mapped seismic horizons PG&E (2013)

5 5 Offshore faults from 3D seismic investigations Activity assessed where Pleistocene strata are present PG&E (2012, LESS 3D draft)

6 6 Offshore faults from hi-res multibeam bathymetric data Activity assessed from fault connectivity along strike and from microseismicity

7 7 Onshore faults Mapping and map compilation mostly from LTSP Includes updates: AMEC (2011), Wiegers (2009) PG&E ONSIP Draft Lettis et al. (2004)

8 8 Onshore faults, constraints on activity Trenches and road logs from LTSP

9 9 Onshore faults, constraints on activity Trenches and road logs from LTSP Marine terraces deformed New data constraints

10 10 Principal stress and strain axes for assessment of fault kinematics Shown at N 15 E Preferred orientation is N10-20 E

11 Seismogenic Depth 11 Modeled as 12 km for all faults but Hosgri. Standard measure of seismogenic depth is D90 (e.g., CEUS SSHAC SSC report; 2012) D90 for events near DCPP is 10.5 km. D95 is 12.5 km (from Hardebeck 2014 catalog) Large earthquakes on Hosgri (>100 km) may extend to greater depth of 15 km Analogy of Landers mainshock/aftershock deepening (Rolandone et al., 2004) Sensitivity analyses show very little effect on hazard

12 12 Constraints on fault model, Sections A-A': PXP, Wilmar Avenue fault exposure, MdO MB MPT LOF B-B':Los Osos Trenches, San Luis Bay fault onshore PB PXP C-C': Memorial Park Terrace, DCPP D-D': Morro Bay, Montaña de Oro terraces, Seismic line 103/104, Pt. Buchon 3D LESS SLB WAF

13 13 Fault Model 1, Outward Vergent Ranges uplifted by partitioned strain on moderately dipping oblique reverse fault system Most dextral of the three models. Most fault continuity Similar to LTSP and Shoreline Report SSC models Possible Analog: 1957 Gobi Altay earthquake, Bogd Range, Mongolia

14 14 Los Osos and SWBZ faults are high angle reverse faults. Obliquity varies by strike West Huasna fault is reverse-oblique fault bounding uplift of Santa Lucia Range

15 15 Irish Hills uplifted by reverse deformation on Los Osos and San Luis Bay faults Los Osos fault decreases in dip where range widens Possible strain partitioning between rangebounding reverse faults and steeper strike slip faults within the range Northward continuation of Oceano fault at depth accommodates uplift of San Luis Hill

16 16 Offshore terrace data suggest uplift boundary associated with San Luis Bay fault extends westward across Shoreline fault. Possibly expressed as distributed zone of deformation No deformation of Memorial Park terrace (PG&E, 2012) suggests Los Osos may also be blind here

17 17 Westernmost part of range uplifted only by Los Osos fault with Hosgri as backstop San Luis Bay fault has died by thispoint More westward trend of West Huasna fault suggests gentler dip in NNE-directed strain regime Line of section crosses Los Osos where it steps northward to offshore trace

18 18 Video animation

19 19 Quaternary Fault Map

20 20 Fault Model 2, Southwest Vergent Gently dipping SW vergent ramp accommodates uplift of Irish Hills. Ramp Offsets/deflects Shoreline fault Deeper detachment explains uplift west of Pt. San Luis. Los Osos fault is locally faulted axial surface/backthrust Incorporates concepts from of San Luis Range fault and deep detachment that were part of some proponent models Possible Analog: San Simeon (2003)

21 21 Uplift of Edna block by gently dipping Oceano fault, which splays from Oceanic- West Huasna at depth. Underlying ramp explains uplift of marine terraces in Edna Valley (PG&E, 2012) Wilmar Avenue and Los Osos east bound pop-up in hanging wall.

22 22 Uplift of Irish Hills by gently dipping San Luis Bay fault, which splays from detachment at depth. Los Osos fault is axial surface or minor backthrust that marks uplift boundary Continuation of detachment beyond San Luis Bay fault explains low rate of uplift at San Luis Hill.

23 23 SW vergent model is paired with limiting minimum dip model for Hosgri East-dipping faults conceptually similar. Distributed zone of deformation west of Shoreline fault updip of San Luis Bay fault tip

24 24 SW vergent model provides poor explanation for subsidence in Morro Bay Possibility shown here is localized flat in geometry of detachment May be related to end of N-vergent Los Osos offshore.

25 25 Video animation

26 26 Quaternary Fault Map

27 27 Fault Model 3, Northeast Vergent NE vergent Los Osos ramp accommodates uplift of Irish Hills. Splays from Hosgri. SW vergent ramp accommodates uplift of Edna block. Splays from West Huasna Opposite vergence Implies tear coincident with SLO Creek. Partly supported by jog in syncline axis Possible Analog: Pie De Palo (Regnier et al., 1992)

28 Pie de Palo Event (Regnier et al., 1992) 28

29 29 Pie de Palo Event (Regnier et al., 1992)

30 30 Uplift of Edna block by gently dipping Oceano fault, which splays from Oceanic- West Huasna at depth. Underlying ramp explains uplift of marine terraces in Edna Valley (PG&E, 2012) Wilmar Avenue and Los Osos east bound pop-up in hanging wall.

31 31 Uplift of Irish Hills by gently dipping Los Osos fault. San Luis Bay fault either fold hinge or backthrust. P(s)<1. San Miguelito and Edna fault are inactive here. Poor fits for this model because they would be separated from southward continuation by tear.

32 32 Offshore terrace data suggest uplift boundary associated with San Luis Bay fault extends westward across Shoreline fault. Possibly expressed as distributed zone of deformation No deformation of Memorial Park terrace (PG&E, 2012) suggests Los Osos may also be blind here

33 33 Westernmost part of range uplifted only by Los Osos fault, possibly splaying from Hosgri at depth More westward trend of West Huasna fault suggests gentler dip in NNE-directed strain regime Line of section crosses Los Osos where it steps northward to offshore trace

34 34 Video animation

35 35 Accounting of fault parameters Do these models adequately characterize the CBR of TDI for PSHA? Fault dip Style of faulting Seismogenic probability Fault width Depth to top of rupture Fault lengths Part of CBR of TDI is that fault lengths are not meaningful in an interconnected system of faults like this. Fault lengths are characterized downstream in Mmax assessments. Rupture lengths are handled downstream in Mchar assessments. Also tracking ground motion parameters for interface with GMC team: Hanging wall effect, Rjb, Rrup, Rx, Ry

36 36 Parameter Values, Hosgri Fault Model: 1. Outward vergent 2. SW vergent 3. NE Vergent Weighted Weight 0.4 Weight 0.3 Weight 0.3 Range mean* Hosgri Center East West Center East West Center East West Summary Mean Dip Dip Direction E W E E E E N/A N/A N/A P(S) Style of faulting SS SS SS SS SS SS SS SS SS Width (12 km depth) Width (15 km depth) Depth to top (Ztor) NE Vergent SW Vergent Outward Vergent

37 Parameter Values, Shoreline fault 37 Model: 1. Outward vergent 2. SW vergent 3. NE Vergent Weighted Weight 0.4 Weight 0.3 Weight 0.3 Range mean Shoreline SH+SS+SE SH+SS+SE SH+SS+SE Summary Dip Dip Direction 0.0 P(S) Style of faulting SS SS SS Depth to top (Ztor) Mean Width NE Vergent SW Vergent Outward Vergent

38 Parameter Values, San Luis Bay fault 38 Model: 1. Outward vergent 2. SW vergent 3. NE Vergent Weighted Weight 0.4 Weight 0.3 Weight 0.3 Range mean San Luis Bay BR/BO+BE BR/BO+BE BR/BO+BE Summary Dip Dip Direction N N N P(S) Style of faulting R R R Depth to top (Ztor) Mean Width NE Vergent SW Vergent Outward Vergent

39 Parameter Values, Los Osos fault 39 Model: 1. Outward vergent 2. SW vergent 3. NE Vergent Weighted Weight 0.4 Weight 0.3 Weight 0.3 Range mean Los Osos LC+LM+LV+LE LC+LM+LV+LE LC+LM+LV+LE Summary Dip Dip Direction SW SW SW P(S) Style of faulting RL/R-O R R Depth to top (Ztor) Mean Width Section D-D NE Vergent SW Vergent Outward Vergent

40 Parameter Values, Edna fault 40 Model: 1. Outward vergent 2. SW vergent 3. NE Vergent Weighted Weight 0.4 Weight 0.3 Weight 0.3 Range mean Edna N/A N/A LC+ED+LE Summary Dip Dip Direction SW P(S) Style of faulting RL Depth to top (Ztor) Mean Width Section B-B NE Vergent SW Vergent Outward Vergent

41 41 Parameter Values, San Miguelito fault Model: 1. Outward vergent 2. SW vergent 3. NE Vergent Weighted Weight 0.4 Weight 0.3 Weight 0.3 Range mean San Miguelito MN+MF MN+MF MN Summary Dip Dip Direction NE P(S) Style of faulting RL Depth to top (Ztor) Mean Width Section B-B NE Vergent SW Vergent Outward Vergent